1. Field of the Invention
The present invention relates to a semiconductor device capable of communicating wirelessly and a manufacturing method of the semiconductor device.
2. Description of the Related Art
A semiconductor device typified by a wireless tag capable of wirelessly communicating identification data or the like has been put into practical use in various fields, and the market thereof is likely to further increase as a new type of communication information terminal. The wireless tag is also called an RFID (Radio Frequency Identification) tag or an IC tag. The wireless tag in practical use usually has an antenna and an IC chip formed by using a semiconductor substrate.
An AC signal received by an antenna is rectified by a rectifier element such as a diode in a wireless tag, and then sent to the subsequent stages. In general, a transistor is used as the diode for rectification. A signal from the wireless tag can be read from the change in the impedance of the antenna caused by controlling a voltage applied to the antenna in the wireless tag. A transistor is also used as a switching element for controlling a voltage applied to the antenna.
In the case of such a transistor used as a diode or a switching element being formed by using a semiconductor substrate, there is a problem in that a large amount of current flows between a P-type base region and a drain region of the transistor depending on the polarity of an AC signal. The mechanism thereof is specifically described with reference to FIG. 12.
FIG. 12 shows a structure of a transistor formed on a single crystalline substrate. A transistor 7002 is formed in a P-type base region 7001 of a semiconductor substrate and includes N-type regions 7003 and 7004 each of which functions as a source region or a drain region. It is assumed that the P-type base region 7001 of the semiconductor substrate is connected to a ground potential and the N-type region 7003 is electrically connected to an antenna 7005. In that case, the N-type region 7003 and the P-type base region 7001 form a rectifying contact, thereby a parasitic diode 7006 is formed.
Accordingly, in the case of a potential supplied from the antenna 7005 to the N-type region 7003 being higher than the ground potential, a current does not flow easily from the N-type region 7003 to the P-type base region 7001. Meanwhile, in the case of a potential supplied from the antenna 7005 to the N-type region 7003 being lower than the ground potential, a current flows easily from the P-type base region 7001 to the N-type region 7003, which may lead to the degradation or even destruction of the transistor 7002.
In order to solve the aforementioned problem, Patent Document 1 discloses a structure in which a guard band applied with a bias through high resistance is provided at the periphery of a MOSFET.    [Patent Document 1] Japanese Patent Laid-Open No. 2000-299440